Lynn Sr.'s grandfather is an unnamed minor character in The Loud House, and is the father of Lynn Sr.'s father, Lynn Sr.'s grandfather, and the children's great-grandfather. He makes his only physical appearance in "Vantastic Voyage", albeit in a flashback.
He was possibly born in Royal Woods, and his son was Lynn Loud Sr.'s father. He hand-me-downed Vanzilla to his son, but this seems unlikely, as that would suggest that it goes farther back than that type of vehicle would have existed.
His appearance looks similar to a 1950s greaser. He has black hair, that has been applied with grease, and styled into a pompadour. He wears a black leather jacket, with a white shirt underneath it, blue jeans, a black belt, and black boots. He has similar facial features to his grandson.